VAC (Valve Amplification Company’s) iQ automatic bias system, as exemplified by the Statement 450 iQ monoblock power amplifier (US$58,000 each) is said to be the result of 18 years of research and development by the engineers at VAC. It is most suitable for high-power fixed-bias Class AB designs which can undergo a significant drift in the DC operating point when driven hard. It aims to maintain each power tube at its optimal DC bias current regardless of how loudly or softly the music is playing. Bob Carver’s DC restoration circuit aims to address pretty much the same issue. However, the cost of the VAC iQ circuitry is significant. The cost differential between the manual biasing Statement 450 and 450 iQ monoblocks is US$14,000.